BLE stack loads old CCCD values after removing bonds on client side and reconnect

[vitaliy2034]

I'm testing BLE secure communication with the nRF52840DK device and I have encountered a problem with bonds. I use modified example from BLE fundamental course, in which I added ability to determine if we connected to new or bonded client. The following steps will better describe my issue:

1. Perform connection, pairing, and bonding with the nRF52840DK(Nordic_LBS).
   
2. Subscribe to Button characteristic notification(write to its CCCD 0x0001 value).
   
3. Disconnect from nRF52840DK(Nordic_LBS).
4. Remove bonds on the client's side. (Bonds on nRF52840DK(Nordic_LBS) still present):
   
5. Perform connection with the same nRF Connect client. As you can see, nRF52840DK(Nordic_LBS) still assume that it bonded with client.
   
6. Check Button characteristic CCCD value.

Expected result: 0x0000

Actual result: 0x0001

Same situation occurs even if in step 5 I perform connection, pairing, bonding again with the device. nRF connect logs and modified example attached.

Fullscreen nRF Connect Logs.txt Download

nRF Connect, 2025-04-29
Nordic_LBS (C5:9D:AD:DC:BB:A3)
V	10:54:20.015	Connecting to C5:9D:AD:DC:BB:A3...
D	10:54:20.015	gatt = device.connectGatt(autoConnect = false, TRANSPORT_LE, preferred PHY = LE 1M)
D	10:54:20.300	[Broadcast] Action received: android.bluetooth.device.action.ACL_CONNECTED
D	10:54:20.301	[Callback] Connection state changed with status: 0 and new state: CONNECTED (2)
I	10:54:20.301	Connected to C5:9D:AD:DC:BB:A3
V	10:54:20.302	Discovering services...
D	10:54:20.302	gatt.discoverServices()
D	10:54:20.425	[Callback] Services discovered with status: 0
I	10:54:20.425	Services discovered
V	10:54:20.426	Generic Attribute (0x1801)
- Service Changed [I] (0x2A05)
   Client Characteristic Configuration (0x2902)
- Client Supported Features [R W] (0x2B29)
- Database Hash [R] (0x2B2A)
Generic Access (0x1800)
- Device Name [R] (0x2A00)
- Appearance [R] (0x2A01)
- Peripheral Preferred Connection Parameters [R] (0x2A04)
Nordic LED Button Service (00001523-1212-efde-1523-785feabcd123)
- Button [N R] (00001524-1212-efde-1523-785feabcd123)
   Client Characteristic Configuration (0x2902)
- LED [W] (00001525-1212-efde-1523-785feabcd123)
D	10:54:20.426	gatt.setCharacteristicNotification(00002a05-0000-1000-8000-00805f9b34fb, true)
D	10:54:20.427	gatt.setCharacteristicNotification(00001524-1212-efde-1523-785feabcd123, true)
I	10:54:20.983	PHY updated (TX: LE 2M, RX: LE 2M)
V	10:54:22.807	Starting pairing...
D	10:54:22.807	device.createBond()
D	10:54:22.872	[Broadcast] Action received: android.bluetooth.device.action.BOND_STATE_CHANGED, bond state changed to: BONDING (11)
D	10:54:23.016	[Broadcast] Action received: android.bluetooth.device.extra.PAIRING_VARIANT, pairing variant: PIN
I	10:54:25.497	Connection parameters updated (interval: 47.5ms, latency: 0, timeout: 420ms)
D	10:54:40.213	[Broadcast] Action received: android.bluetooth.device.action.BOND_STATE_CHANGED, bond state changed to: BONDED (12)
I	10:54:40.213	Device bonded
V	10:55:08.990	Enabling notifications for 00001524-1212-efde-1523-785feabcd123
D	10:55:08.990	gatt.setCharacteristicNotification(00001524-1212-efde-1523-785feabcd123, true)
D	10:55:08.992	gatt.writeDescriptor(00002902-0000-1000-8000-00805f9b34fb, value=0x0100)
I	10:55:09.054	Data written to descr. 00002902-0000-1000-8000-00805f9b34fb, value: (0x) 01-00
A	10:55:09.054	"Notifications enabled" sent
V	10:55:09.056	Notifications enabled for 00001524-1212-efde-1523-785feabcd123
V	10:55:23.185	Reading descriptor 00002902-0000-1000-8000-00805f9b34fb
D	10:55:23.185	gatt.readDescriptor(00002902-0000-1000-8000-00805f9b34fb)
I	10:55:23.256	Read Response received from descr. 00002902-0000-1000-8000-00805f9b34fb, value: (0x) 01-00
A	10:55:23.256	"Notifications enabled" received
V	10:56:07.030	Disconnecting...
D	10:56:07.030	gatt.disconnect()
D	10:56:07.037	[Callback] Connection state changed with status: 0 and new state: DISCONNECTED (0)
I	10:56:07.037	Disconnected
D	10:56:08.067	[Broadcast] Action received: android.bluetooth.device.action.ACL_DISCONNECTED
V	10:58:35.899	Removing bond information...
D	10:58:35.899	device.removeBond() (hidden)
D	10:58:35.983	[Broadcast] Action received: android.bluetooth.device.action.BOND_STATE_CHANGED, bond state changed to: NONE (10), reason: REMOVED (9)
I	10:58:35.983	Bond information lost, reason: REMOVED (9)
D	10:58:37.758	gatt.close()
D	10:58:37.761	wait(200)
V	10:58:37.964	Connecting to C5:9D:AD:DC:BB:A3...
D	10:58:37.964	gatt = device.connectGatt(autoConnect = false, TRANSPORT_LE, preferred PHY = LE 1M)
D	10:58:38.219	[Broadcast] Action received: android.bluetooth.device.action.ACL_CONNECTED
D	10:58:38.235	[Callback] Connection state changed with status: 0 and new state: CONNECTED (2)
I	10:58:38.235	Connected to C5:9D:AD:DC:BB:A3
V	10:58:38.254	Discovering services...
D	10:58:38.254	gatt.discoverServices()
D	10:58:38.346	[Callback] Services discovered with status: 0
I	10:58:38.346	Services discovered
V	10:58:38.349	Generic Attribute (0x1801)
- Service Changed [I] (0x2A05)
   Client Characteristic Configuration (0x2902)
- Client Supported Features [R W] (0x2B29)
- Database Hash [R] (0x2B2A)
Generic Access (0x1800)
- Device Name [R] (0x2A00)
- Appearance [R] (0x2A01)
- Peripheral Preferred Connection Parameters [R] (0x2A04)
Nordic LED Button Service (00001523-1212-efde-1523-785feabcd123)
- Button [N R] (00001524-1212-efde-1523-785feabcd123)
   Client Characteristic Configuration (0x2902)
- LED [W] (00001525-1212-efde-1523-785feabcd123)
D	10:58:38.349	gatt.setCharacteristicNotification(00002a05-0000-1000-8000-00805f9b34fb, true)
D	10:58:38.355	gatt.setCharacteristicNotification(00001524-1212-efde-1523-785feabcd123, true)
I	10:58:38.910	PHY updated (TX: LE 2M, RX: LE 2M)
I	10:58:43.424	Connection parameters updated (interval: 47.5ms, latency: 0, timeout: 420ms)
V	10:58:53.575	Reading descriptor 00002902-0000-1000-8000-00805f9b34fb
D	10:58:53.575	gatt.readDescriptor(00002902-0000-1000-8000-00805f9b34fb)
I	10:58:53.636	Read Response received from descr. 00002902-0000-1000-8000-00805f9b34fb, value: (0x) 01-00
A	10:58:53.636	"Notifications enabled" received
D	10:58:53.639	gatt.setCharacteristicNotification(00001524-1212-efde-1523-785feabcd123, true)
V	10:58:53.641	Notifications enabled for 00001524-1212-efde-1523-785feabcd123

l6_e3_sol.zip

Please advise if it is possible to handle that situation on the side. Or should it be handled on the client side and how?

[Hung Bui]

Hi Biliy, 

I believe it's not a bug but a feature. 
When you connect to a previously bonded device and the device now has removed bond with you, you are not expected to remove the previous bond and remove the gatt cache (CCCD cache) 
The reason for that is that an attacker can easily spoof the peer device address and pretend that the bond has been removed (and maybe request a new bond). 

You can either allow overwriting using this config CONFIG_BT_SMP_ALLOW_UNAUTH_OVERWRITE (only for just work) or request end user proactively remove bond on the device itself. 

So from my point of view GATT cache should not be automatically removed. It should only be remove when delete bond button is pressed/selected on the device itself.